Automatic signal transmission control circuit



Sept 6 1938 l D. THIERBACH v2,129,074

AUTOMATIC SIGNAL TRANSMISSION CONTROL CIRCUIT Filed Feb. 21, 1935 l' AMPM/m "41. V l V `4Q42 lf www 72 soa/ms -H l l l 6 Fi I 52 QE Mgg-wz Y En i M Q` /vmoL 5 C 5gg nga/1 mm1/Nor D|ETWALD THlERAcH 71) RECWF/ER BY )Lg ATTORNEY Patented Sept. 6, 1938 UNITED STATES PATENT GFFHQE AUTOMATIC SIGNAL TRANSMISSION CON- TROL CIRCUIT many Application February 21,1935, Serial No. 7,468 In Germany March 23, 1934 1 Claim.

The present invention relates to automatic signal transmission control systems, and more particularly to a system wherein the signal feeding path of the signal network is regulated.

For the purpose of equalizing fadings, for amplitude limitation, level stabilization and volume-ratio regulation in music transmission installations, control or regulating means have been used in the past in which the Voltage regulation is 10 accomplished by the aid of controllable non-linear resistances. The latter may consist, for instance,

of electron tubes or dry (cuprous-oXide) rectiiiers.

The circuit scheme usually is so chosen that the non-linear resistances are cut in the circuit, or l5 transmission path, either in the form of shunt or series elements. By virtue of amplitude dependence it has thus been feasible to act upon the transmission measure as a function of the ampli tudes fed to the resistances.

It has also been suggested in the prior art to control the non-linear resistances by direct current. In this instance, for example, in the rear of, or above, the amplifier to be regulated part of the energy was shunted or branched off, then 25 rectiiied, and finally fed to the non-linear resistance for the purpose of causing a shift in its working point and thus of its resistance value. The control of non-linear resistances has been insured also in this manner that control po- 30 tentials adjusted manually was fed to them, the operation then being, of course, fundamentally speaking the same as in automatic regulation. What is important in all instances is that the resistance is influenced by the aid of control voltages 35 which are varied at the rhythm, or rate, of the regulation. Generally speaking the frequency of the regulative action is substantially lower than that of the signals to be transmitted.

The kind of non-linear resistance that has here- 40 tofore been used for regulation changed its resistance not only at the rhythm of the regulating voltages supplied thereto, but also at the frequency of the transmitted signal current, and the consequence was non-linear distortion. The 45 latter was liable to assume considerable and serious proportions whenever large amplitude Variations were fed to the resistances, and when the lack of linearity of the resistances was very great with a view to insuring adequate regula- 50 tion sensitiveness or response. Hence, the circuit schemes known in the art were found to be unserviceable in instances where it was found to be imperative that the distortion factor should not undergo any substantial increase as a result of 56 the regulating action.

Now, these shortcomings are obviated according to the present invention by that a kind of regulating resistance is used in which the resistivity, as a result of the action of a control quantity, such as a regulating voltage, undergoes alterations only with such sluggishness that it acts like a linear resistance so far as the useful, or working, currents that are to be transmitted are concerned. The resistances, to be used, respond to, and follow, the comparatively slow controlling direct current Voltage variations, but not the essentially more rapid fluctuations of the signal currents to be transmitted. Inasmuch as the difference between the control frequency and the signal frequencies, as before indicated, is generally speaking fairly large, it is found to be comparatively easy to satisfy such conditions as are made regarding the regulating resistances.

What may be considered. useful for the sluggish resistances to be employed for the purpose here concerned are resistances which experience marked changes of resistance upon being heated. What may be particularly recommended for this object are the so-called hot conductors, say, resistances made from uranium oxide in vacuo which have a high negative temperature coefficient. These resistances must be so dimensioned that their time-constant is greater than the length of a period of one of the lowest useful frequencies to be handled or transmitted. It is also possible to use resistances possessing a positive temperature coefficient, and among these may be mentioned standard incandescent (glow) lamps of the metal-filament or tungsten type, unless the regulating range to be covered is large.

The regulating resistance upon which for regulation a regulable direct current Voltage is impressed is combined suitably with fixed resistances; that is to say, resistances whose resistivity does not undergo any iiuctuations, to result in voltage dividers, the consumer or load device being united either with the fixed or with the Variable resistance of the said voltage divider. In lieu of voltage dividers, it would be feasible to connect in series With the consumer also multipole structures whose series, or shunt, elements are made up of controllable resistances. If the voltage regulation is to be of a kind dependent upon the frequency, then the variable resistances must be suitably combined with the resistances whose values are a function of the frequency. If the internal resistance of the source of current furnishing the voltage to be regulated is high enough then it will be found sufficient to connect the regulating resistance in the form of a simple parallel resistance ahead of the consuming device. What is thus obtained is a regulable voltage division without the use of distinct series resistance.

Finally, it is also possible, with a view to securing high regulating response or sensitivity, to dispose a plurality of regulating resistances in cascade, say, a plurality of quadripoles made up of the variable regulator resistance in the form oi series and shunt elements.

A number of practical embodiments are shown in the drawing by Way of example. Fig. 1 illustrates the use of a regulator resistance having a negative temperature coefficient, Figs. 2 and 3 comprise the use of resistances having a positive temperatur-e coefficient. Figs. 4 and 5 are concerned with the use of resistances with negative and positive temperature coecients, respectively, in four-pole schemes.

The voltage to be regulated in all instances is to be ied in, or applied across, the terminals Al and Bl, while at the amplier output end A2-B2 the regulated voltage may be taken off. In the circuit organization shown in Fig. 1, the regulating resistance -R, say in the form of a hot conductorhaving a negative temperature coefficient, as described above, is connected to the voltage source in series with an ohmic resistance Rv. The input of the amplifier V to be regulated is united by way of the blocking condensers C with the terminals of the regulating resistance -R. In the output circuit of the arnplier V a part of the energy is shunted off, and from this energy is ltered out, by the aid of a filter F, a control or piloting frequency specially transmitted for regulating purposes, and, finally, after rectification in rectifier G, fed to the regulator resistance. The choke-coils D serve to keep the signal currents away from the rectier circuit, while condensers C are provided with the end in View to preclude the controlling direct current from. the input circuit of the amplier.

If in this circuit organization the output poten- Y tial of the amplifier undergoes a rise, then also the current coming from the rectier will grow. As a result of the negative temperature coeflicient of the variable resistance, the resistance value of the regulating resistance for the signal currents decreases with the consequence that also the voltage impressed upon the amplifier will be lowered. 1n other words, level stabilization is feasible with a circuit scheme of this kind.

Fig. 2, by way of example, shows in what way, by the same circuit organization, and by the aid oi a resistance possessing a positive temperature coefficient, regulation of the level is accomplished. What is here necessary is that with growth of output voltage of the amplifier the direct current voltage fed to the regulating resistance becomes lower. For this purpose, between the rectifier G, whose outputcurrent is smoothed by the lter S, and the regulating resistance there is interposed an amplifier tube R. With growing amplitude, the grid biasing voltage of the tube R is shifted into the negative region so that the plate current of the tube R becomes less. As a result, also, the resistance Value of the regulating resistance decreases for the signal currents. If the input of the amplifier to be regulated is not connected with the regulating resistance, but rather with the xed resistance Rv, then level stabilization is feasible as shown in Fig. 3 by the aid of a resistance +R having a positive temperature coefficient without having recourse t0 an amplifier tube R.

Fig. 4 shows a quadripole arrangement which is interposed between the input of the amplier to be regulated and the source of current AI-Bl furnishing the voltage which is to be regulated.

The series elements of the resistance consist of xed resstances Rv. The variable resistance -R is included in the quadripole in the form of a shunt element. The control voltage designed to act upon the regulating resistance is fed in at points Sl--S2.` The condensers C serve also in this scheme for the purpose of precluding the control current from the circuit carrying the signal current. When a regulating resistance with a negative temperature coeicient is employed, the damping oi the quadripole increases with increasing control potential.

The same regulation is practicable with a quadripole arrangement shown in Fig. 5 comprising the use of a regulating resistance +R having a positive temperature coefcient.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modications may be made without departing from the scope of my invention as set forth in the appended claim.

What is claimed is:r

In a high frequency signal transmission system of the type including an amplier, a source of high frequency signal energy for the amplifier, said energy including energy of a control frequency, a signal shunting path connected across said source, said path including a resistive element comprising a filament of uranium oxide in vacuo whose resistance has a temperature coefficient of a negative sign, said element having a suiciently high inertia at the frequency of said signal energy to impart a constant resistance characteristic thereto at said signal frequency, the amplifier input circuit being connected to said source and across at least a portion of said shunting path, means for deriving a direct current from the energy of Vsaid control frequency, and means for applying said direct current to said resistive element.

DIETWALD THIERBACH. 

